Low exhaust temperature electrically heated particulate matter filter system

ABSTRACT

A system includes a particulate matter (PM) filter, a sensor, a heating element, and a control module. The PM filter includes with an upstream end that receives exhaust gas, a downstream end and multiple zones. The sensor detects a temperature of the exhaust gas. The control module controls current to the heating element to convection heat one of the zones and initiate a regeneration process. The control module selectively increases current to the heating element relative to a reference regeneration current level when the temperature is less than a predetermined temperature.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/972,322 filed on Sep. 14, 2007. The disclosure of the aboveapplication is incorporated herein by reference.

STATEMENT OF GOVERNMENT RIGHTS

The disclosure was produced pursuant to U.S. Government Contract No.DE-FC-04-03 AL67635 with the Department of Energy (DoE). The U.S.Government has certain rights in this disclosure.

FIELD

The present disclosure relates to particulate matter (PM) filters, andmore particularly to electrically heated PM filters.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

Engines such as diesel engines produce particulate matter (PM) that isfiltered from exhaust gas by a PM filter. The PM filter is disposed inan exhaust system of the engine. The PM filter reduces emission of PMthat is generated during combustion.

Over time, the PM filter becomes full. During regeneration, the PM maybe burned within the PM filter. Regeneration may involve heating the PMfilter to a combustion temperature of the PM. There are various ways toperform regeneration including modifying engine management, using a fuelburner, using a catalytic oxidizer to increase the exhaust temperaturewith after injection of fuel, using resistive heating coils, and/orusing microwave energy. The resistive heating coils are typicallyarranged in contact with the PM filter to allow heating by bothconduction and convection.

Diesel PM combusts when temperatures above a combustion temperature suchas 600° C. are attained. The start of combustion causes a furtherincrease in temperature. While spark-ignited engines typically have lowoxygen levels in the exhaust gas stream, diesel engines havesignificantly higher oxygen levels. While the increased oxygen levelsmake fast regeneration of the PM filter possible, it may also pose someproblems.

PM reduction systems that use fuel tend to decrease fuel economy. Forexample, many fuel-based PM reduction systems decrease fuel economy by5%. Electrically heated PM reduction systems reduce fuel economy by anegligible amount. However, durability of the electrically heated PMreduction systems has been difficult to achieve.

SUMMARY

In one embodiment, a system is provided that includes a particulatematter (PM) filter, a sensor, a heating element, and a control module.The PM filter includes an upstream end that receives exhaust gas, adownstream end and multiple zones. The sensor detects a temperature ofthe exhaust gas. The control module controls current to the heatingelement to convection heat one of the zones and initiate a regenerationprocess. The control module selectively increases current to the heatingelement relative to a reference regeneration current level when thetemperature is less than a predetermined temperature.

In other features, a method includes providing a particulate matter (PM)filter that includes an upstream end that receives exhaust gas, adownstream end and multiple zones. A temperature of the exhaust gas isdetected. Current to a heating element is controlled to convection heatone of the zones and initiate a regeneration process. Current to theheating element is selectively increased relative to a referenceregeneration current level when the temperature is less than apredetermined temperature.

In still other features, a system includes a PM filter, a sensor, aheating element, and a control module. The PM filter includes anupstream end that receives exhaust gas, a downstream end and multiplezones. The sensor detects an exhaust gas temperature of the exhaust gas.The control module selectively activates and adjusts output of theheating element to convection heat one of the zones and initiate aregeneration process. The control module selectively adjusts operationof the heating element to increase temperature of a portion of theupstream end to a regeneration temperature level that supportscombustion propagation along the PM filter from the upstream end to thedownstream end when the exhaust gas temperature is less than apredetermined temperature.

In yet features, the systems and methods described above are implementedby a computer program executed by one or more processors. The computerprogram can reside on a computer readable medium such as but not limitedto memory, nonvolatile data storage, and/or other suitable tangiblestorage mediums.

Further areas of applicability of the present disclosure will becomeapparent from the detailed description, the claims and the drawings. Itshould be understood that the detailed description and specific examplesare intended for purposes of illustration only and are not intended tolimit the scope of the disclosure.

DRAWINGS

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

FIG. 1 is a functional block diagram of an exemplary engine including aparticulate matter (PM) filter with a zoned inlet heater that is spacedfrom the PM filter;

FIG. 2 is a flowchart illustrating a PM filter regeneration method inaccordance with an embodiment of the present disclosure;

FIG. 3 illustrates a PM filter with incomplete regeneration due to coldexhaust temperatures;

FIG. 4 illustrates exemplary zoning of the zoned inlet heater of theelectrically heated PM filter of FIG. 1 in further detail;

FIG. 5 illustrates an exemplary resistive heater in one of the zones ofthe zoned inlet heater of FIG. 3;

FIG. 6 illustrates the electrically heated PM filter having a zonedelectric heater that is spaced from the PM filter;

FIG. 7 illustrates heating within a zoned electric heater; and

FIG. 8 is a flowchart illustrating steps performed by the control moduleto regenerate the PM filter.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is notintended to limit the present disclosure, application, or uses. Itshould be understood that throughout the drawings, correspondingreference numerals indicate like or corresponding parts and features.

As used herein, the term module refers to an Application SpecificIntegrated Circuit (ASIC), an electronic circuit, a processor (shared,dedicated, or group) and memory that execute one or more software orfirmware programs, a combinational logic circuit, and/or other suitablecomponents that provide the described functionality.

Referring now to FIG. 1, an exemplary diesel engine system 10 isschematically illustrated in accordance with the present disclosure. Itis appreciated that the diesel engine system 10 is merely exemplary innature and that the zone heated particulate filter regeneration system11 described herein can be implemented in various engine systemsimplementing a particulate filter. Such engine systems may include, butare not limited to, gasoline direct injection engine systems andhomogeneous charge compression ignition engine systems. For ease of thediscussion, the disclosure will be discussed in the context of a dieselengine system.

A turbocharged diesel engine system 10 includes an engine 12 thatcombusts an air and fuel mixture to produce drive torque. Air enters thesystem by passing through an air filter 14. Air passes through the airfilter 14 and is drawn into a turbocharger 18. The turbocharger 18compresses the fresh air entering the system 10. The greater thecompression of the air generally, the greater the output of the engine12. Compressed air then passes through an air cooler 20 before enteringinto an intake manifold 22.

Air within the intake manifold 22 is distributed into cylinders 26.Although four cylinders 26 are illustrated, the systems and methods ofthe present disclosure can be implemented in engines having a pluralityof cylinders including, but not limited to, 2, 3, 4, 5, 6, 8, 10 and 12cylinders. It is also appreciated that the systems and methods of thepresent disclosure can be implemented in a V-type cylinderconfiguration. Fuel is injected into the cylinders 26 by fuel injectors28. Heat from the compressed air ignites the air/fuel mixture.Combustion of the air/fuel mixture creates exhaust. Exhaust exits thecylinders 26 into the exhaust system 27.

The exhaust system 27 includes an exhaust manifold 30, a dieseloxidation catalyst (DOC) 32, and a particulate matter (PM) filterassembly 34 with a zoned inlet heater 35. Optionally, an EGR valve (notshown) re-circulates a portion of the exhaust back into the intakemanifold 22. The remainder of the exhaust is directed into theturbocharger 18 to drive a turbine. The turbine facilitates thecompression of the fresh air received from the air filter 14. Exhaustflows from the turbocharger 18 through the DOC 32, through the zonedheater 35 and into the PM filter assembly 34. The DOC 32 oxidizes theexhaust based on the post combustion air/fuel ratio. The amount ofoxidation increases the temperature of the exhaust. The PM filterassembly 34 receives exhaust from the DOC 32 and filters any sootparticulates present in the exhaust. The zoned inlet heater 35 is spacedfrom the PM filter assembly 34 and heats the exhaust to a regenerationtemperature as will be described below.

A control module 44 controls the engine and PM filter regeneration basedon various sensed information. More specifically, the control module 44estimates loading of the PM filter assembly 34. When the temperature ofexhaust gas from the engine 12 is less than a predetermined level andwhen the estimated loading is at a predetermined level and/or when theexhaust flow rate is within a desired range, current is controlled tothe PM filter assembly 34 via a power source 46 to initiate theregeneration process. The duration of the regeneration process may bevaried based upon the estimated amount of particulate matter within thePM filter assembly 34.

Current is applied to the zoned heater 35 during the regenerationprocess. More specifically, the energy heats selected zones of theheater 35 of the PM filter assembly 34 for predetermined periods,respectively. Exhaust gas passing through the heater 35 is heated by theactivated zones. The heated exhaust gas travels to the downstream filterof PM filter assembly 34 and heats the filter by convection. Theremainder of the regeneration process is achieved using the heatgenerated by the heated exhaust passing through the PM filter.

The above system may include various sensors 60. The sensors 60 may beused to determine exhaust flow levels, exhaust temperature levels,exhaust pressure levels, oxygen levels, intake air flow rates, intakeair pressure, intake air temperature, engine speed, EGR information,etc. An exhaust flow sensor 62, an exhaust temperature sensor 64,exhaust pressure sensors 66, oxygen sensor 68, an EGR sensor 70, anintake air flow sensor 72, an intake air pressure sensor 74, an intakeair temperature sensor 76, and an engine speed sensor 78 are shown.Sensors 80 may be exhaust temperature and/or pressure sensors. Sensor 82may be an engine speed sensor.

Referring now to FIG. 2, a logic flow diagram illustrating a PM filterregeneration method is shown.

In one embodiment, regeneration of the PM filter is performed withoutassistance from the associated engine. In other words, air flow, oxygenlevels, fuel injection, and exhaust gas recirculation (EGR) are notadjusted to assist the regeneration process.

During an electrically heated PM filter mode, the current supplied toheater (heating element(s)) is adjusted to provide a heating temperaturethat is based on soot loading, oxygen levels in the exhaust, exhausttemperatures, exhaust flow, etc. Voltage and/or ON time of the heater(heater element(s)) may be adjusted in addition to or as an alternativeto the adjustment of current. A look-up table may be used to provide theappropriate heater current, voltage and/or ON time levels.

When temperature of an input portion of a PM filter associated with aselected zone (“burn zone”) is below a temperature for properregeneration, the heater element current is increased. This increasesheating element temperatures and thus the input temperature of the burnzone. The temperature of the heating element and/or the input portionmay increase above a predetermined peak PM filter operating temperature.

A PM filter may have a predetermined peak operating temperature, whichmay be based on a current temperature of an exhaust or an exhaust gas inan exhaust system. The peak operating temperature may be associated witha point of potential PM filter degradation. For example, a PM filter maybegin to breakdown at operating temperatures greater than 800° C. whenexhaust temperatures are greater than approximately 300° C. The peakoperating temperature may vary for different PM filters. The peakoperating temperature may be associated with an average temperature of aportion of the PM filter or an average temperature of the PM filter as awhole.

In step 100, control begins and proceeds to step 102. In step 102,control determines if regeneration is needed. If regeneration is neededcontrol proceeds to step 104.

In step 104, control may select one or more zones for regeneration. Instep 106, control determines temperature of an exhaust or of an exhaustgas. One or more of the temperature sensors described above may be usedto generate an exhaust gas temperature signal. The temperature signalmay indicate temperature of an exhaust/exhaust gas upstream ordownstream from a PM filter. The temperature signal may also oralternatively indicate temperature of the PM filter and/or exhaust gaswithin the PM filter.

In step 108, when the temperature(s) of step 106 are less than apredetermined temperature level, control proceeds to step 112, otherwisecontrol proceeds to step 110. For example, when the exhaust gastemperature of an exhaust gas that is upstream from the PM filter isless than approximately 300° C., control proceeds to step 112.

In step 110, regeneration of the selected zone(s) is performed. Thisregeneration may include the increasing of a burn zone temperature forthe selected zone(s) first predetermined burn zone temperature level.The regeneration may include steps 312-324 described below. The firstpredetermined burn zone temperature level may correspond with a firstheating element output level, current level, voltage level and/or ONtime level. The predetermined burn zone temperature level may alsocorrespond with a reference regeneration output level, a referenceregeneration current level, a reference regeneration voltage level, areference regeneration ON time level, etc. For example only, the firstpredetermined burn zone temperature level may be approximately between700°-900° C.

In step 112, regeneration of the selected zone(s) is performed. Thisregeneration may include the increasing of a burn zone temperature forthe selected zone(s) to a second predetermined burn zone temperaturelevel. The regeneration may include steps 312-324 described below. Thesecond predetermined burn zone temperature level is greater than thefirst predetermined burn zone temperature level. The secondpredetermined burn zone temperature level may be provided by increasingcurrent, voltage and/or ON time of the selected heating element(s) tolevels greater than provided in step 110. For example only, the firstpredetermined burn zone temperature level may be approximately between900°-1300° C.

The current, voltage and/or ON time levels of steps 110 and 112 may beset based on the temperature(s) of step 106, as well as information fromother sensors, such as from the sensors 60 of FIG. 1. The current,voltage and/or ON time levels of steps 110 and 112 may also be set basedon detected and/or predicted soot levels in the PM filter. The current,voltage and/or ON time levels are set to assure that combustionpropagation travels from an upstream end to a downstream end of the PMfilter and is not extinguished.

In step 114, control determines whether additional zones need to beregenerated. Control returns to step 104 when additional zones are to beregenerated. Otherwise control ends.

Referring now to FIG. 3, a PM filter is shown with incompleteregeneration due to cold exhaust temperatures. When exhaust temperaturesare less than or equal to approximately 300° C., the exothermic reactionin a PM filter during regeneration may become increasingly extinguishedaxially along the PM filter. Cold exhaust gas tends to collapse thethermal propagation wave as it propagates down the PM filter. When theexhaust temperature is too low, the heated area of the PM filter shrinksin size due to exposure of the outer edge of a combustion area of thepropagation wave to cold exhaust gas.

It is common for a diesel engine to operate and provide exhausttemperatures of approximately between 150-300° C. Thus, should aregeneration process be initiated with a heating element temperaturenear or below a recommended peak operating temperature, the regenerationprocess may be incomplete. A substantial amount of soot within the PMfilter may not be burned off, as shown in FIG. 3.

In FIG. 3, zones of a PM filter 130 are shown and labeled 1-5 on aninput (upstream end) 131 of the PM filter 130. The PM filter of FIG. 3is provided as an example to illustrate a result of an exothermicreaction being extinguished during a regeneration process. As anexothermic reaction propagates along a PM filter it may be extinguisheddue to low temperatures of an exhaust gas and/or PM filter and/or thelack of energy provided to initiate the exothermic reaction. The darkareas 132 of the cross-sectional sides 134 of the PM filter 130represent the remaining soot in the PM filter 130. The remaining soot isa result of an exothermic reaction being extinguished during aregeneration process. The amount of soot remaining increases towards theoutput (downstream end) 136 of the PM filter 130.

To improve regeneration, when exhaust temperatures are approximately300° C. or less, heating element current, voltage and/or ON time isadjusted to increase temperature of a portion of an upstream end of a PMfilter above a normal predetermined peak operating temperature. Thenormal predetermined peak operating temperature may refer to a peakoperating temperature of the PM filter as a whole.

The heating element temperatures are increased such that soot combustionrobustly propagates down the length of the PM filter without beingextinguished. The combustion temperature is increased enough such thatthe flamefront propagates down the PM filter channels without affectingsize of the heated area of the flamefront. In one embodiment, theheating element temperatures are increased for one or more zones orportions (pieces) of one or more zones above a peak operatingtemperature. The peak operating temperature is a recommended overallpeak operating temperature for the PM filter. Thus, although the peakoperating temperature for a portion of the PM filter is above therecommended peak operating temperature, the average overall temperatureacross the PM filter is less than the peak operating temperature. Forthis reason, the internal expansion pressures within the PM filter donot exceed a pressure threshold associated with potential PM filterdegradation.

The temperature of the heating elements associated with the heatedzone(s) or zone portion(s) may be increased to approximately 900-1300°C. In one embodiment, the heating element temperatures are increased toapproximately between 1000-1200° C. This increase may be performedwithout any engine assistance or air flow, oxygen level, fuel injection,and exhaust gas recirculation (EGR) adjustment. However, engineassistance may be performed depending upon the situation.

The heating element temperatures may be increased based on soot loading,oxygen levels in the exhaust, exhaust temperatures, exhaust flow, etc.As an example, when a high air flow rate is present, heater current mayincrease, since less heat is resident to the input of a PM filter. Alook-up table may be used to provide the appropriate heater currentlevel and/or heater current level increase. The current levels may bedifferent depending upon the zone, the zone portion, the number of zonesor zone portions, and the location and relative positioning thereof.

In one embodiment, regeneration is performed one zone at a time. Inanother embodiment, regeneration is performed for multiple zoneportions. In yet another embodiment, the total heated area during anyone regeneration process of a PM filter is approximately 20%±5% of thefront input cross-sectional area of the PM filter. Thus, regenerationmay be performed approximately five times to remove soot from all of thezones of the PM filter 130. In still another embodiment, outside zonesalong a perimeter of a PM filter are regenerated prior to regenerationof internal zones.

The amount of fuel consumption associated with the above-describedregeneration process is negligible or approximately zero. This approachleverages soot energy to regenerate a PM filter. Regeneration time isminimal due to soot oxidation rates at high temperatures.

Referring now to FIG. 4, another exemplary zoned inlet heaterarrangement is shown. A center portion may be surrounded by a middlezone including a first circumferential band of zones. The middle portionmay be surrounded by an outer portion including a second circumferentialband of zones.

In this example, the center portion includes zone 1. The firstcircumferential band of zones includes zones 2 and 3. The secondcircumferential band of zones comprises zones 1, 4 and 5. As with theembodiment described above, downstream portions from active zones areregenerated while downstream portions from inactive zones provide stressmitigation. As can be appreciated, one of the zones 1, 2, 3, 4 and 5 canbe activated at a time. Others of the zones remain inactivated.

The electrical heater may be spaced from the PM filter. In other words,the electric heater may be located in front of the PM filter but not incontact with the downstream PM filter. The heater selectively heatsportions of the PM filter. The PM filter may be mounted close enough tothe front of the PM filter to control the heating pattern. The length ofthe heater is set to optimize the exhaust gas temperature.

Thermal energy is transmitted from the heater to the PM filter by theexhaust gas. Therefore the PM filter is predominately heated byconvection. The electrical heater is divided in zones to reduceelectrical power required to heat the PM filter. The zones also heatselected downstream portions within the PM filter. By heating only theselected portions of the filter, the magnitude of forces in thesubstrate is reduced due to thermal expansion. As a result, higherlocalized soot temperatures may be used during regeneration withoutdamaging the PM filter.

The PM filter is regenerated by selectively heating one or more of thezones in the front of the PM filter and igniting the soot using theheated exhaust gas. When a sufficient face temperature is reached, theheater is turned off and the burning soot then cascades down the lengthof the PM filter channel, which is similar to a burning fuse on afirework. In other words, the heater may be activated only long enoughto start the soot ignition and is then shut off. Other regenerationsystems typically use both conduction and convection and maintain powerto the heater (at lower temperatures such as 600 degrees Celsius)throughout the soot burning process. As a result, these systems tend touse more power than the system proposed in the present disclosure.

The burning soot is the fuel that continues the regeneration. Thisprocess is continued for each heating zone until the PM filter iscompletely regenerated.

The heater zones are spaced in a manner such that thermal stress ismitigated between active heaters. Therefore, the overall stress forcesdue to heating are smaller and distributed over the volume of the entireelectrically heated PM filter. This approach allows regeneration inlarger segments of the electrically heated PM filter without creatingthermal stresses that damage the electrically heated PM filter.

Referring now to FIG. 5, an exemplary resistive heater 200 arrangedadjacent to one of the zones (e.g. zone 3) from the firstcircumferential band of zones in FIG. 3 is shown. The resistive heater200 may comprise one or more coils that cover the respective zone toprovide sufficient heating.

Referring now to FIG. 6, the PM filter assembly 34 is shown in furtherdetail. The PM filter assembly 34 includes a housing 200, a filter 202,and the zoned heater 35. The heater 35 may be arranged between a laminarflow element 210 and a substrate of the filter 202. For PM filters withan end plug near the input of the PM filter, the heating elementtemperatures of the heater 35 are increased to increase temperatures ofthe PM filter downstream from the end plug. This allows thermal energyto propagate down the PM filter walls and/or channels. An electricalconnector 211 may provide current to the zones of the PM filter assembly34 as described above.

As can be appreciated, the heater 35 may be spaced from the filter 202such that the heating is predominantly convection heating. Insulation212 may be arranged between the heater 35 and the housing 200. Exhaustgas enters the PM filter assembly 34 from an upstream inlet 214 and isheated by one or more zones of the PM filter assembly 34. The heatedexhaust gas travels a distance and is received by the filter 202. Theheater 35 may be spaced from and not in contact with the filter 202.

Referring now to FIG. 7, heating within the PM filter assembly 34 isshown in further detail. Exhaust gas 250 passes through the heater 35and is heated by one or more zones of the heater 35. The heated exhaustgas travels a distance “d” and is then received by the filter 202. Thedistance “d” may be ½″ or less. The filter 202 may have a central inlet240, a channel 242, filter material 244 and an outlet 246 locatedradially outside of the inlet. The filter may be catalyzed. The heatedexhaust gas causes PM in the filter to burn, which regenerates the PMfilter. The heater 35 transfers heat by convection to ignite a frontportion of the filter 202. When the soot in the front face portionsreaches a sufficiently high temperature, the heater is turned off.Combustion of soot then cascades down a filter channel 254 withoutrequiring power to be maintained to the heater.

Referring now to FIG. 8, steps for regenerating the PM filter are shown.In step 300, control begins and proceeds to step 304. If controldetermines that regeneration is needed in step 304, control selects oneor more zones in step 308 and activates the heater for the selected zonein step 312. In step 316, control estimates a heating period (PM filterON time) sufficient to achieve a minimum filter face temperature basedon at least one of current of PM filter heating element(s), voltage ofPM filter heating element(s), exhaust flow, exhaust temperature, etc.The minimum face temperature should be sufficient to start the sootburning and to create a cascade effect. For example only, the minimumface temperature may be set to 700 degrees Celsuis or greater. In analternate step 320 to step 316, control estimates current and voltageneeded to achieve minimum filter face temperature based on apredetermined heating period, exhaust flow and exhaust temperature.

In step 324, control determines whether the heating period is up. Ifstep 324 is true, control determines whether additional zones need to beregenerated in step 326. If step 326 is true, control returns to step308. Otherwise control ends.

The above-described steps of FIGS. 2 and 8 are meant to be illustrativeexamples; the steps may be performed sequentially, synchronously,simultaneously, continuously, during overlapping time periods or in adifferent order depending upon the application.

In use, the control module determines when the PM filter requiresregeneration. Alternately, regeneration can be performed periodically oron an event basis. The control module may estimate when the entire PMfilter needs regeneration or when zones within the PM filter needregeneration. When the control module determines that the entire PMfilter needs regeneration, the control module sequentially activates oneor more of the zones at a time to initiate regeneration within theassociated downstream portion of the PM filter. After the zone or zonesare regenerated, one or more other zones are activated while the othersare deactivated. This approach continues until all of the zones havebeen activated. When the control module determines that one of the zonesneeds regeneration, the control module activates the zone correspondingto the associated downstream portion of the PM filter needingregeneration.

The present disclosure may substantially reduce the fuel economypenalty, decrease tailpipe temperatures, and improve system robustnessdue to the smaller regeneration time.

Those skilled in the art can now appreciate from the foregoingdescription that the broad teachings of the disclosure can beimplemented in a variety of forms. Therefore, while this disclosureincludes particular examples, the true scope of the disclosure shouldnot be so limited since other modifications will become apparent to theskilled practitioner upon a study of the drawings, the specification,and the following claims.

1. A system comprising: a particulate matter (PM) filter comprises anupstream end that receives exhaust gas, a downstream end and a pluralityof zones; a sensor that detects a temperature of said exhaust gas; aheating element; and a control module that controls current to saidheating element to convection heat one of said zones and initiate aregeneration process, wherein said control module selectively increasescurrent to said heating element relative to a reference regenerationcurrent level when said temperature is less than a predeterminedtemperature.
 2. The system of claim 1 comprising a plurality of heatingelements, wherein said control module selectively activates one of saidplurality of heating elements to convection heat one of said zones. 3.The system of claim 1 wherein said heating element is spaced apredetermined distance upstream from said upstream end.
 4. The system ofclaim 1 wherein said control module decreases current to said heatingelement when said temperature exceeds a threshold.
 5. The system ofclaim 1 wherein said control module increases said current to saidheating element to increase temperature of a portion of said upstreamend to a regeneration temperature level that supports combustionpropagation along said PM filter from said upstream end to saiddownstream end.
 6. The system of claim 5 wherein said control moduledeactivates said heater element after said temperature of said portionreaches said regeneration temperature level.
 7. The system of claim 5wherein said control module supports said regeneration process byadjusting said current and activation ON time of said heating elementand without adjusting exhaust gas flow, engine intake airflow, fuelinjection operation, and exhaust gas recirculation.
 8. The system ofclaim 1 wherein said regeneration temperature level is greater than amaximum operating temperature of said PM filter that corresponds with anexhaust gas temperature that is greater than said predetermined level.9. The system of claim 1 wherein said control module increases saidcurrent to said heating element to increase temperature of a portion ofsaid upstream end to a regeneration temperature level that supportscombustion propagation along said PM filter from said upstream end tosaid downstream end while said heater element is deactivated.
 10. Thesystem of claim 1 wherein said control module sets said current at afirst level when said temperature is greater than said predeterminedtemperature and increases said current to a second level when saidtemperature is less than said predetermined temperature, and whereinsaid first level corresponds with said reference regeneration currentlevel.
 11. The system of claim 1 wherein said control module increasessaid current to a predetermined current level based on said temperature.12. The system of claim 1 wherein said control module determines aheating period to heat a portion of said upstream end to a minimumfilter face temperature, and wherein said control module activates saidheating element for said heating period.
 13. The system of claim 12wherein said heating period is determined based on at least one ofcurrent and voltage of said heating element.
 14. The system of claim 12wherein said heating period is determined based on at least one ofexhaust flow and said temperature.
 15. The system of claim 1 whereinsaid control module adjusts said current based on a soot level of saidPM filter, an exhaust flow level, and an oxygen level.
 16. A methodcomprising: providing a particulate matter (PM) filter that comprises anupstream end that receives exhaust gas, a downstream end and a pluralityof zones; detecting a temperature of said exhaust gas; controllingcurrent to a heating element to convection heat one of said zones andinitiate a regeneration process; and selectively increasing current tosaid heating element relative to a reference regeneration current levelwhen said temperature is less than a predetermined temperature.
 17. Themethod of claim 16 comprising: setting said current at a first levelwhen said temperature is greater than said predetermined temperature;and increasing said current to a second level when said temperature isless than said predetermined temperature, wherein said first levelcorresponds with said reference regeneration current level.
 18. A systemcomprising: a particulate matter (PM) filter comprises an upstream endthat receives exhaust gas, a downstream end and a plurality of zones; asensor that detects an exhaust gas temperature of said exhaust gas; aheating element; and a control module that selectively activates andadjusts output of said heating element to convection heat one of saidzones and initiate a regeneration process, wherein said control moduleselectively adjusts operation of said heating element to increasetemperature of a portion of said upstream end to a regenerationtemperature level that supports combustion propagation along said PMfilter from said upstream end to said downstream end when said exhaustgas temperature is less than a predetermined temperature.
 19. The systemof claim 18 wherein said control module when adjusting said operation ofsaid heating element increases at least one of current, voltage and ONtime of said heating element.
 20. The system of claim 18 wherein saidcontrol module sets said output at a first level when said temperatureis greater than said predetermined temperature and increases said outputto a second level when said temperature is less than said predeterminedtemperature.